1. Technical Field
The present invention relates to improvement of a piezoelectric vibration piece and a piezoelectric device which receives the piezoelectric vibration piece in a package or a case.
2. Related Art
FIG. 7 is a schematic plan view illustrating an example of a piezoelectric vibration piece which has been conventionally used in a piezoelectric device and FIG. 8 is a schematic cross-sectional view taken along line A-A of FIG. 7.
In Figures, a piezoelectric vibration piece 1 is formed to have an illustrated outer shape by etching a piezoelectric material such as quartz and includes a rectangular base 2 and a pair of vibration arms 3 and 4 which extends from the base 2 to a right side of FIG. 7. Elongate grooves 3a and 4a are formed in principal surfaces (front/rear surfaces) of the vibration arms.
In other words, electrodes 5 and 6 applied with driving voltages to have opposite polarities are provided in the base 2.
The electrode 5 is led to an inner surface of the elongate groove 3a provided in the vibration arm 3 and a side surface 4b facing an inner surface of the elongate groove 4a of the vibration arm 4.
The electrode 6 is led to the inner surface of the elongate groove 4a provided in the vibration arm 4 through a side electrode 6a provided in a side surface 3b facing the inner surface of the elongate groove 3a of the vibration arm 3 and a base electrode 6b provided in a principal surface of the base 2 such that the electrode 6 is not short-circuited to the electrode 5.
In addition, since an electrode must not be provided in a crotch portion 2a between the vibration arms 3 and 4, leading the side electrode 6a to the base electrode 6b is accomplished by forming an electrode 6c connected to the side electrode 6a on the principal surface (front/rear surface) of a sidewall 3c of the vibration arm 3 and connecting the electrode 6c to the base electrode 6b. 
An electric field can be generated between the electrodes provided in the inner surfaces of the elongate grooves 3a and 4a and the electrodes provided in the side surfaces 3b and 4b of the vibration arms 3 and 4 to reduce a crystal impedance value (hereinafter, referred to as “CI value”). Thus, it is possible to miniaturize the piezoelectric vibration piece.
However, in the miniaturized piezoelectric vibration piece, the above-mentioned leading of the electrodes is not facilitated. In particular, since the width W1 of the sidewall 3c of the vibration arm 3 is very small, it is difficult to form the electrode 6c on the principal surface of the sidewall 3c, without coming into contact with the electrode provided in the inner surface of the elongate groove 3a. 
Accordingly, a piezoelectric vibration piece 10 illustrated in FIG. 9 which is a partial enlarged view illustrating the periphery of a root of a vibration arm was suggested (for example, JP-A-2002-76827).
In the piezoelectric vibration piece 10, since the width W2 of an elongate groove 13 located at a joint of a vibration arm 14 is less than the width W3 of the front end of the elongate groove 13, it is possible to surely form an electrode 12 on a sidewall without coming into contact with an electrode provided in the inner surface of the elongate groove 13 by the smaller width.
However, since a recent piezoelectric vibration piece has been newly miniaturized, it is difficult to accurately form an electrode on a principal surface of a sidewall having a very small width in a vibration arm. For example, since the width of the electrode 6c of the principal surface of the sidewall 3c illustrated in FIG. 7 is at most 3 μm, the electrode 6c may not be formed on the principal surface of the sidewall 3c and thus the electrode 6c and the electrode 6b on the base 2 may not be connected to each other. Although the electrode 6c can be accurately formed on the principal surface of the sidewall 3c, the electrode 6c on the principal surface of the sidewall and the electrode 6b on the base 2 may be disconnected from each other due to slight deviation of a position of the electrode 6b on the base 2 connected to the electrode 6c. 
In addition, according to the recent miniaturization of the piezoelectric vibration piece, disconnection may occur even in the piezoelectric vibration piece 10 illustrated in FIG. 9. For example, a position of the electrode 12 on the principal surface of the sidewall is deviated from a position 12a indicated by a dotted line of FIG. 9 and thus the electrode 12 on the principal surface of the sidewall may be disconnected from the side electrode 11.
Moreover, although the position of the electrode 12 on the principal surface of the sidewall is slightly deviated, the disconnection between the side electrode 11 and the electrode 12 on the sidewall can be avoid by more decreasing the width W2 of the elongate groove 13 illustrated in FIG. 9 and more increasing the width of the electrode 12 on the principal surface of the sidewall. However, when the width W2 of the elongate groove 12 is too small, the CI value increases.